1. Field of the Invention
This invention is generally concerned with blending and processing allotropic forms of silica, alumina and zirconia with those active catalysts commonly employed in petroleum "cracking" processes to form improved binder matrices. More particularly it is concerned with the rapid introduction of catalyst additive concentrates into a bulk of resident catalyst mass without encountering unacceptable attrition or elutriation losses.
2. Description of the Prior Art
The history of the petroleum industry and, consequently, of refining technology, has been that of originally making use of a small part of petroleum and then finding a use for the remainder. Later the industry learned how to chemically alter components of crude petroleum in order to accommodate competing market demands. The first such alteration was accomplished by thermal decomposition in the early 1930's. However, thermal decomposition left much to be desired; in fact it probably created more problems than it solved. In any event, the next most important step in this art was the development of gas oil in the presence of naturally occurring clays, such as kaolins, hollysite and others, in an atmosphere of its own vapor. Later developments included the introduction of synthetic catalysts such as silica-alumina and silica-magnesia and combinations of these materials with the previously employed naturallyoccurring clays. Still later it was found that certain crystalline zeolites, notably the y-fajusites, were particularly effective cracking catalyst components. This technology produced major strides in the amount and quality of those components of "synthetic crude" thus produced. Reasearch continues to this day to bring this basic process to the highest levels of precision.
Another major innovation took place with the introduction of the "fluidized bed" to burn coke residues which result from cracking reactions off of the catalyst particles. Synthetic catalysts are employed in fluidized beds as well as in fixed beds and in moving beds, for such varied purposes as octane improvement, sulfur removal, isomerization, etc. Various changes in the basic catalyst formulation were made in order to encourage cracking processes to take place at various conditions of temperature and pressure as well as in atmospheres of different vapors. Consideration of all of these factors has progressively resulted in the use of catalysts of vastly greater complexity. At present, complexes of alumina, aluminosilicate, silica, chromia, zirconia, gallium, germanium, etc., are generally regarded as the most effective catalysts. However, heretofore, their formulations have not fully utilized the benefits following from the use of colloidal ingredients in their binder formulations. That is to say most prior art catalyst compositions are of two general types: (1) those that are aggregates of various catalyst components which are generally held together by noncolloidal forms of known binding agents and (2) those that are formed "in situ" by growing crystalline lattices in preformed clay particles. In either case, even minor changes in known catalyst ingredients e.g., noncolloidal silica or noncolloidal alumina binding agents and/or minor changes in the ways in which the ingredients are formulated can have profound effects upon the efficacy and profitability of any given cracking operation.
Hence, new catalysts are sometimes "tailor-made" for specific duties by making subtle changes in catalyst formulations. To this end, zeolite type catalysts have proven to be particularly useful; they have been used in such varied operations as hydrocracking, alkylation, dealkylation, transalkylation, isomerization and polymerization. By way of example, U.S. Pat. No. 3,703,886 to Argauer discloses a whole class of small crystalline aluminosilicates, designated ZSM-5, which have demonstrated high selectivites in catalytic cracking processes. Low-soda exchanged Y-zeolite catalysts and ultra-stable Y-zeolite catalysts have these same desirable attributes. Use of these kinds of aluminosilicates has however presented some problems. For example, catalysts of these kinds are generally characterized by their being in the range of about 0.5 to about 4 microns in crystalline size. This characteristic renders them unsuitable for direct introduction into commercial cracking plants because of the difficulties associated with separting such small particles from vapor streams leaving reaction systems such as catalytic crackers. This is principally because well-designed cyclones are only capable of retaining or collecting particles larger than about 20 microns. Because of this limitation, there is a considerable need for binding these small crystalline catalytic materials into larger attrition-resistant aggregate particles. A second consideration in binding these aggregates is to provide particles with sufficient density to be retained in the commercial cracking unit. It is also important that the individual crystalline particles be well-dispersed in the matrix and that the matrix have sufficient pore volume to provide ready access to the crystalline catalyst particles.
These are some of the problems which are particularly addressed by this patent disclosure. In the past, the direct address of these problems has been through the use of varying proportions of different chemical species to formulate more durable catalyst matrices. These problems also have been addressed, incidentally, in the course of various chemical treatments primarily intended to implement or improve the catalytic activity of various zeolites. This has been done both by reducing catalytic reactivity when it is excessive and by increasing it when it is insufficient. Such reactivity oriented modifications are of some relevance to the attrition issue dealt with in this patent disclosure since a reduction in catalytic activity may, under certain circumstances, be accompanied by an improvement in other characteristics of the catalyst, including increased resistance to attrition and/or aging. U.S. Pat. No. 4,594,332, for example, clearly recognizes this relationship; it teaches production of hard, fracture-resistant catalysts from zeolites of the pentasil family by a process in which water, an organic additive such as hydroxyethylcellulose--which serves to increase viscosity--and a silicate are added to zeolite particles. The resultant material is then molded and calcined to produce a catalyst having increased fracture-resistance.
Thus to the extent they impart fracture-resistance to catalyst particles (assuming there are no concomitant unacceptable losses in reactivity or classification due to the sweeping action of the reaction mass through the catalyst mass), all of the above noted materials and processes represent improvements in the art of making catalysts more resistant to attrition, density changes, aging and the like. However, there still is room for further improvements and advances.
In all catalytic cracking operations in which the catalyst moves, there are two principal mechanisms by which losses occur to the bulk mass of a catalyst. It occurs first by reason of different density. Typically, classification and sequestration is caused by the action of a mass of reaction vapors sweeping through and separating catalyst particles according to their density differenes. The second loss mechanism is caused by the same forces acting upon particles of different size and/or shape to cause interparticle impacts which tend to shatter the catalyst. This in turn results in small fragments which are lost e.g., when particles less than 20 microns are not retained by a cyclone. It is therefore very important in all such processes to reduce such losses to at least economically acceptable levels.
It should also be noted that current catalytic cracking technology and practices no longer are content with employment of a "best compromise" catalyst formulation. Rather, a base mass of active catalyst is, in practice, constantly being adjusted by the addition of as many as 5 or 6 different additive concentrates. Each concentrate can have a profound influence on a specific area of catalyst activity and/or performance e.g., completion of coke oxidation during regeneration, limitation of hydrogen production, promotion of olefin formation, promotion of isomerization, etc. However, for such introductions of concentrates to be effective and feasible, that is to say, not requiring vast amounts of equipment, labor and constat addition and removal of catalysts, sampling, testing and readjustment of the bulk composition, several salient features and circumstances must be in operation. First, the active specific ingredient of the additive must be highly concentrated in the additive material. Second, it must be added rapidly and evenly. It is these presisting requirements and circumstances which continue to create a need for materials, such as those described in this patent disclosure, which are capable of being quickly introduced into a catalytic system without experiencing unacceptable attrition losses.